The disclosure of Japanese Patent Application No. 2001-022088 filed on Jan. 30, 2001, and No. 2001-375469 filed on Dec. 10, 2001 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to contact lens to be worn on a cornea of a human eye, which has a substantially circular optical zone and an annular peripheral zone disposed around the optical zone. More particularly, the present invention is concerned with such a contact lens, which is novel in construction and which is capable of enhancing lens wearing comfort as felt by a lens wearer.
2. Description of the Related Art
There is known a contact lens which is worn on a surface of a cornea of a human eye for treating myopia, hyperopia, astigmatism, presbyopia and the like. Since the contact lens is worn on the cornea accompanied with contact thereof with very sensitive surfaces of the cornea and eyelids of a lens wearer, there is a great need to enhance lens wearing comfort as felt by the lens wearer.
In general, the contact lens includes a substantially circular central optical zone serving for transmitting light to a pupil, and an annular peripheral zone disposed radially outwardly of the optical zone and serving for placing the contact lens on a predetermined position on the cornea. The peripheral zone is designed to permit a good circulation of tear fluid existing between the cornea and the contact lens. The optical zone has a back surface that is formed in a concave shape whose curvature is made substantially equal to that of the cornea of the lens wearer, so that the back surface of the optical zone of the contact lens may suitably fit the shape of the cornea of the lens wearer. This radius of curvature of the back surface of the optical zone of the lens is generally referred to as a base curve.
However, the conventional contact lens as described above gives rise to a problem of discomfort as felt by the contact lens wearer when he or she wear the lens, although degrees of the discomfort may vary among individual wearers. In particular, a conventional contact lens of hard or rigid type gives the lens wearer a relatively large wearing discomfort. Thus, the conventional contact lens is insufficient to assure a good wearing comfort thereof.
In addition, the conventional hard type contact lens is likely to suffer from a problem that dusts or other floating objects in the atmosphere are introduced into the tear fluid existing between the contact lens and the cornea. This results in significantly deterioration of the lens wearing comfort as felt by the lens wearer, and sometimes gives rise to a burden on the lens wearer to remove the contact lens to wash it.
It is therefore an object of this invention to provide a contact lens which is novel in structure, and which is capable of eliminating or minimizing a discomfort as felt by a contact lens wearer when he or she wear the contact lens, and assuring an improved wearing condition of the lens, while preventing an entrance of the dust or the like into a tear fluid portion between the lens and the cornea.
The above and/or other objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whose specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A contact lens comprising: (a) an optical zone having a generally circular shape; (b) an peripheral zone having a generally annular shape and located around the optical zone; and (c) an intermediate zone having a generally annular shape and interposed between the optical and peripheral zones, wherein the intermediate zone has a back surface provided with a convex portion formed in at least one diametrical position thereof and extending in a circumferential direction thereof with an outwardly curved surface in cross section taken in a plane parallel to a diametric direction of the contact lens.
In the contact lens according to this mode of the invention, the convex portion is disposed radially outwardly of the optical zone and extends in the circumferential direction of the contact lens so as to surround the optical zone. With the contact lens worn on a cornea of a lens wearer, this convex portion protrudes toward the cornea from a posterior surface of the contact lens, and is located closely adjacent to a surface of the cornea. A tear fluid layer existing between the posterior surface of the contact lens and the cornea is partially narrowed and restricted at a portion where the convex portion is opposed to the cornea. Therefore, the convex portion smoothly leads the posterior surface of the contact lens to be located adjacent to and positioned relative to the surface of the cornea with its smooth outwardly curved surface having no peak or junction.
Accordingly, the contact lens of the invention permits an improved lens wearing comfort as felt by the lens wearer. In addition, since the convex portion partially narrows the tear fluid layer, unfavorable entrance of dusts or other floating objects in the atmosphere into the tear fluid layer is effectively restricted or limited, thus assuring an enhanced usability of the contact lens. It is presumed that these advantages of the present contact lens, namely, the improved lens wearing comfort and the limitation of the entrance of the dusts into the tear fluid layer, stem from the following technical basis or reasons: (i) a barrier effect owing to a convex configuration of an alignment portion (that is contact with or most closely adjacent to the surface of the cornea) of the contact lens, i.e., the convex portion formed in the back surface of the intermediate zone that is opposed to and protrudes toward the surface of the cornea; and (ii) a stress diffusion effect owing to the outwardly curved surface of the convex portion of the intermediate zone, which permits the convex portion to be opposed to the surface of the corneal with a smooth surface.
A result of extensive research and study of the inventors reveals that the contact lens of this mode of the invention exhibits a high positioning stability on the cornea, while ensuring a reduced amount of displacement of the contact lens relative to the cornea when the lens wearer blinks, for example. Therefore, the contact lens of this mode of the invention enables to decrease or moderate discomfort as felt by the lens wearer due to friction between the contact lens and eyelid and/or cornea caused by the displacement of the contact lens relative to the cornea, resulting in further improved lens wearing comfort as felt by the lens wearer. This improvement of the lens wearing comfort may also stem from that the limited entrance of the dusts or other floating objects into a clearance between the contact lens and the cornea via the tear fluid existing and circulated between the contact lens and the cornea due to the presence of the narrowed portion of the tear fluid layer, as well as the above-indicated reduced displacement of the contact lens relative to the cornea.
Described more specifically, the contact lens of this mode of the invention is worn on the cornea and pressed onto the cornea upon application of an external pressing force thereon. Such an external pressing force is applied on an anterior surface of the contact lens, by the eyelids of the lens wearer, when the lens wearer blinks. As a result, the posterior surface of the contact lens is located adjacent to the surface of the cornea as close as possible, making it possible to restrict the displacement of the contact lens relative to the cornea. In this respect, the convex portion has the outwardly curved surface with no peak or junction, thus minimizing or eliminating adverse effects of the convex portion on the corner. Further, the convex portion does not adversely effect on the optical zone, since the convex portion is located radially outward of the optical zone.
This mode of the present invention is preferably applicable to a rigid gas permeable lens (RGPL) so that a sufficient amount of oxygen permeated through the contact lens is applied to the cornea, even if an amount of circulation of the tear fluid between the cornea and the contact lens is decreased. The principle of this mode of the invention is also applicable to a soft contact lens and a hard contact lens, which are made of polymethyl metacrylate (PMMA). In both cases, the contact lens of this mode of the invention is able to enjoy the advantages of the invention as mentioned above. Further, the principle of the present invention may be applicable to various kinds of known contact lens to be worn on the cornea for treating myopia, hyperopia, astigmatism, or the other disability or disease of a person""s eye. The configuration of the convex portion is not particularly limited, but may preferably have a smooth curved surface whose radius of curvature is not too small to form a junction or a peak, so that the contact lens can be worn on the cornea with no or minimized adverse influence due to the contact of the convex portion with the cornea. Preferably, the convex portion is formed in an annular form extending continuously over its entire circumference of the contact lens. In order to regulate the tear fluid circulation between the contact lens and the cornea, this annular convex portion may have at least one cutout formed in a circumferential portion thereof such that the annular convex portion is divided into a plurality of circumferential parts due to the presence of the cutout.
(2) A contact lens according to the above-indicated mode (1), wherein the back surface of the intermediate zone has an inner circumferential portion connected to the optical zone and provided with a radially inner concave portion extending in a circumferential direction thereof with an inwardly curved surface in the diametrical cross section of the contact lens, the inwardly curved surface having a radius of curvature smaller than that of the optical zone and being connected at an outer circumferential portion to said convex portion. The contact lens according to this mode of the invention permits a smooth connection between the optical zone and the convex portion on the posterior surface of the contact lens, thereby providing a smooth surface on the overall back surface of the intermediate zone. This arrangement makes it possible to dimension the convex portion with a sufficiently large height, while assuring an excellent lens wearing comfort, resulting in an improved degree of freedom in designing the convex portion.
The configurations of the convex portion and the radially inner concave portion formed in the back surface of the intermediate zone may be suitably determined taking into account a height or a position of the convex portion, a curvature of the base curve (i.e., a curvature of the back surface of the optical zone) and efficiency in designing and manufacturing the contact lens. For instance, the convex portion and the radially inner concave portion are shaped in the diametrical cross section to have a desired configuration selected from a simple arcuate configuration, conic sections, configurations represented by polynomials of not less than second order, or the like.
(3) A contact lens according to the above-indicated mode (2), wherein the radially inner concave portion formed on the back surface of the intermediate zone is connected at the outer circumferential portion thereof to an inner circumferential portion of the convex portion with a continuous surface which joins to the outer circumferential portion of the radially inner concave portion along knots lying on tangents common to curves of the radially inner concave portion and the continuous surface, and joins to the inner circumferential portion of the convex portion along knots lying on tangents common to curves of the convex portion and the continuous surface. In the contact lens constructed according to this mode of the invention, the radially inner concave portion and the convex portion both formed in the back surface of the intermediate zone are connected to each other without creating any peaks or junctions at a boundary therebetween. This enables the convex portion to have a smoother surface, hence assuring a further improved lens wearing comfort as felt by the lens wearer. It should be appreciated that the continuous surface has a desired radial width that is suitably determined taking into account a desired lens design. It may be possible to form the continuous surface as a point or boundary as seen in the diametric cross section of the contact lens. In this case, the continuous surface lies on tangents common to both curves of the radially inner concave portion and the convex portion.
(4) A contact lens according to the above-indicated mode (2) or (3), wherein the outwardly curved surface of the convex portion and the inwardly curved surface of the radially inner concave portion have respective arcuate configurations in the diametrical cross-section of the contact lens. In the contact lens constructed according to this mode of the invention, the convex portion and the radially inner concave portion are effectively formed such that centers of arcs of said convex portion and said radially inner concave portion are located on the opposite sides of the posterior surface of the contact lens.
In the above-indicated modes (2)-(4), the concave portion may include a plurality of concave parts which are continuously connected to each other in the diametric direction of the contact lens, which have different arcuate configuration, as seen in the diametrical cross section of the lens, whose radiuses of curvatures are different from each other. In this case, the curvatures of the plurality of concave parts vary so as to gradually increase in the radially outward direction of the contact lens, preferably, so that the plurality of concave parts effectively serves for connecting the base curve of the back surface of the optical zone and the convex portion with a smoothly contiguous surface, even if the convex portion protrudes backwards from the back surface of the optical zone with a relatively large amount of height.
(5) A contact lens according to the above-indicated mode (2) or (3), wherein at least one of the outwardly curved surface of the convex portion and the inwardly curved surface of the radially inner concave portion has a configuration represented by any one of a conic section and a polynomial of not less than second order, in the diametrical cross section of the contact lens.
(6) A contact lens according to the above-indicated mode (2) or (3) of the invention, wherein the back surface of the intermediate zone including the convex portion and the radially inner concave portion has a configuration represented by any one of a polynomial and a trigonometric function in the diametrical cross-section of the lens. This arrangement makes it possible to design the entire back surface of the intermediate zone of the contact lens by utilizing only one equation, making it easy to calculate a shape design of the contact lens, while assuring smoothness of the entire back surface of the intermediate zone. For the trigonometric function, a sine function and a cosine function may be preferably used.
(7) A contact lens according to any one of the above-indicated modes (1)-(6), wherein the convex portion formed on the back surface of the intermediate zone is connected at an inner circumferential portion thereof to the optical zone with a first inwardly curve and at an outer circumferential portion thereof to the peripheral zone with a second inwardly curve, the convex portion protruding at least partially toward a back side of the contact lens from both of a radially outward prolongation of the back surface of the optical zone and a radially inward prolongation of the back surface of the peripheral zone in the diametrical cross section of the contact lens. In the contact lens constructed according to this mode of the invention, the optical zone, the intermediate zone and the peripheral zone are smoothly connected one another on the posterior surface of the contact lens in the diametric direction of the contact lens, thus providing a smoothly connected overall posterior surface of the contact lens. This smooth posterior surface of the contact lens effectively prevents or reduces occurrence of stress or stimulation concentration on a local area of the surface of the cornea, resulting in a further improved lens wearing comfort.
(8) A contact lens according to the above-indicated mode (1), wherein the convex portion formed on the back surface of the intermediate zone extends to an inner circumferential portion of the intermediate zone so as to be connected to the optical zone with a continuous surface which joins to the optical zone along knots lying on tangents common to curves of the optical zone and the continuous surface, and joins to the inner circumferential portion of the convex portion along knots lying on tangents common to curves of the convex portion and the continuous surface. This mode of the invention makes it possible to form the convex portion to be located adjacent to a peripheral portion of the optical zone and to be smoothly contiguously connected to the optical zone.
(9) A contact lens according to the above-indicated mode (8), wherein only one of the convex portion is formed on the back surface of the intermediate zone so as to extend over an entire radial length of the intermediate zone. This mode of the invention makes it possible to form the preferable convex portion on the back surface of the intermediate zone, while simplifying the configuration of the back surface of the intermediate zone.
(10) A contact lens according to any one of the above modes (1)-(9), wherein a posterior surface of the contact lens is arranged such that the intermediate zone is connected at an inner circumferential portion thereof to the optical zone with a first continuous surface which joins to the optical zone along knots lying on tangents common to curves of the optical zone and the continuous surface, and joins to the inner circumferential portion of the intermediate zone along knots lying on tangents common to curves of the intermediate zone and the continuous surface, while the intermediate zone is connected at an outer circumferential portion thereof to the peripheral zone with a second continuous surface which joins to the peripheral zone along knots lying on tangents common to curves of the peripheral zone and the continuous surface, and joins to the outer circumferential portion of the intermediate zone along knots lying on tangents common to curves of the intermediate zone and the continuous surface. The contact lens according to this mode of the invention has the posterior surface in which the optical zone, the intermediate zone and the peripheral zone are smoothly connected to one another in the diametrical direction of the contact lens over the substantially entire area of the back surface of the contact lens. This arrangement enables to eliminate or minimize a local interfere between the contact lens and the surface of the corneal, resulting in further improved lens wearing comfort as felt by the lens wearer. It should be appreciated that the first continuous surface may be constituted by common tangent points in which the optical and the intermediate zones are directly connected to each other and lie on tangents common to both curves of the back surfaces of the optical and intermediate zones, or alternatively may be constituted by a curved surface interposed between the optical zone and the intermediate zone and lies on tangents whose slopes are continuously changed over its entire width including connecting points to the optical zone and the intermediate zone as seen in the diametrical cross section of the lens. Likewise, the second continuous surface may be constituted by common tangent points in which the intermediate zones and the peripheral zone are directly connected to each other and lie on tangents common to both curves of the back surfaces of the intermediate and peripheral zones, or alternatively may be constituted by a curved surface interposed between the intermediate zone and the peripheral zone and lies on tangents whose slopes are continuously changed over its entire width including connecting points to the intermediate zone and the peripheral zone as seen in the diametrical cross section of the lens.
(11) A contact lens according to any one of the above-indicated modes (1)-(10), wherein the peripheral zone has a back surface including a plurality of concave parts that have respective arcuate configuration in the diametrical cross section of the contact lens whose radiuses of curvatures are different from each other, the plurality of concave parts being continuously connected to each other in a radial direction of the lens such that curvatures of the plurality of concave parts decrease as radial distances of the plurality of concave parts from the convex portion increase. This arrangement makes it possible to effectively form the peripheral zone in an outer circumferential portion of the posterior surface of the contact lens, even in the case where the convex portion protrudes backwards with a relatively large amount of protrusion (height) backward of the contact lens. In addition, this arrangement is effective to avoid a problem of deterioration of lens wearing comfort due to an increased wall thickness of the peripheral zone.
(12) A contact lens according to the above-indicated mode (9), wherein a back surface of the peripheral zone is formed as an outwardly curved surface or a tapered surface straightly extending radially outwardly so that the back surface of the peripheral zone protrudes backward of the contact lens so as not to exceed a radially outward prolongation of the back surface of the intermediate zone. In the contact lens constructed according to this mode of the invention, a single convex portion is formed over the entire area of the intermediate zone and at least inner circumferential portion of the peripheral zone. This arrangement makes it possible to form the convex portion that extends between the peripheral portion of the optical zone and the peripheral zone with an overall smooth surface.
In the contact lens constructed according to this mode (12) of the invention, the intermediate zone and the peripheral zone may not be separated from each other by a clear boundary formed therebetween, if the same radius of curvature is set to a portion ranging from the outer circumferential portion of the intermediate zone to the inner circumferential portion of the peripheral zone, for example. In this specific case of this mode of the invention, it might be considered that the convex portion is formed on the inner circumferential portion of the peripheral zone that is located adjacent to the peripheral portion of the optical zone. However, the presence of the convex portion disposed radially outward of the optical zone ensures the contact lens of this mode to exhibit the effects of the present invention as described above. Hence, it should be appreciated that the contact lens according to such a specific case of this mode (12) includes the intermediate zone in the form of the convex portion, and is accordingly included within the scope of the invention defined in the following claims.
(13) A contact lens according to any one of the above-indicated modes (1)-(11), wherein at least one of the intermediate zone and the peripheral zone, which are disposed radially outward of the convex portion, is provided with a radially outer concave portion extending in a circumferential direction thereof with an inwardly curved surface in the diametrical cross section of the contact lens, the inwardly curved surface having a radius of curvature smaller than that of the optical zone. In the contact lens constructed according to this mode of the invention, the intermediate or peripheral zone located radially outward of the optical zone protrudes toward the corneal and the sclera of the lens wearer""s eye, making it possible to stably place the contact lens on the cornea such that the peripheral portion of the optical zone is spaced apart from the surface of the cornea with a distance larger than a distance between the central portion of the optical zone and the surface of the cornea. For this characteristic, the contact lens constructed according to this mode (13) is suitably used for in a so-called xe2x80x9corthokeratologyxe2x80x9d treatment. In order to effectively provide a contact lens for the orthokeratology treatment, a difference between the radius of curvature: Ra of the optical zone and the radius of curvature: Rb of the radially outer concave portion is preferably held within a range of xe2x88x921 mm xe2x88x921 mm (xe2x88x921 mmxe2x89xa6(Raxe2x88x92Rb)xe2x89xa6. 1 mm), more preferably is held within a range of xe2x88x920.5 mmxe2x88x920.5 mm (xe2x88x920.5 mmxe2x89xa6(Raxe2x88x92Rb)xe2x89xa6. 0.5 mm). In order to provide a contact lens for an abnormal curvature correction, the radius of curvature: Ra of the optical zone is made smaller than the radius of curvature: Rb of the radially outer concave portion (Ra less than Rb).
(14) A contact lens according to any one of the above-indicated modes (1)-(13), wherein the back surface of the optical zone has a curvature that is made smaller than a curvature of the cornea, and a radially inner portion of the back surface of the intermediate zone located radially inward of the convex portion serves as a tear fluid reserving portion. In this mode of the invention, a central portion of the optical zone is adapted to apply a pressing force on a central portion of the surface of the cornea, to thereby reshaping the cornea. A refractive power of the cornea itself is desirably changed due to the reshaping of the cornea, thus reducing a myopic condition in a so-called xe2x80x9corthokeratologyxe2x80x9d manner. That is, the contact lens according to this mode of the invention is effectively used in the orthokeratology treatment. As disclosed in U.S. Pat. No. 4,952,045, for example, operations, effects or usage of the contact lens in the orthokeratology treatment are well known in the arts. For this reason, no detail description of this matter is provided for the sake of simplicity of the description. In the contact lens according to this mode of the invention, particularly, the central portion of the optical zone and the convex portion, which are to be located most closely adjacent to the cornea, have a smooth surface. Therefore, the present contact lens permits good wearing comfort as felt by the lens wearer and eliminated or reduced adverse effects on the cornea, while exhibiting a desired cornea reshaping effect as a primary effect.
(15) A contact lens according to any one of the above-indicated modes (1)-(14) wherein the peripheral zone has an outer diameter within a range of 8-16 mm. In general, contact lenses have a diameter of 11 mm or smaller. On the other hand, the contact lens according to this mode of the invention enables to have a relatively large diameter thereof. This arrangement assures that the eyelids of the wearer apply a relatively large pressing force on the upper surface of the contact lens, making it possible to position the contact lens on the cornea with further improved stability, and to further enhance lens wearing comfort as felt by the lens wearer, or alternatively making it possible to apply the contact lens to the orthokeratology treatment for further facilitating reshaping of the cornea with enlarged abutting pressure of the contact lens on the cornea. As is understood from the aforementioned description with respect to this mode of this invention, the contact lens of this mode is applicable to a sclera lens as well as the corneal contact lens.
(16) A contact lens according to any one of the above-indicated modes (1)-(15), wherein the optical zone has a radial width within a range of 40-70% of a radius of the contact lens, and the intermediate zone has a radial width within a range of 20-45% of the radius of the contact lens, while the peripheral zone has a radial width within a range of 5-25% of the radius of the contact lens. In the contact lens constructed according to this mode of the invention, the optical zone is able to effectively provide an excellent eyesight or a high degree of acuity of viewing with a suitable amount of light. The intermediate zone has the back surface in which the convex portion and the concave portion (which may formed as needed) are formed with smoothly curved surfaces without abrupt change in their curvature, thereby exhibiting an excellent wearing comfort. Further, the peripheral zone is capable of adjusting a stability of the contact lens on the cornea, a tear fluid circulation capacity of the lens, and a diameter of the lens.
In the contact lens constructed according to any one of the above-indicated modes (1)-(16), the configuration of the optical zone is not particularly limited. For the myopic treatment, the optical zone may preferably have a spherical surface whose curvature is similar to that of the surface of the cornea. For the orthokeratology treatment, the optical zone may preferably have a spherical surface whose curvature is made smaller than that of the surface of the cornea. Alternatively, the optical zone may have the diametrical cross sectional shape in the form of a conic section, e.g., ellipse, parabola, hyperbola, or the like.
The contact lens constructed according to any one of the above-indicated modes (1)-(16) may be manufactured according to various kinds of method of producing hard-type or soft-type contact lenses. For instance, the contact lens of the present invention may be manufactured by molding using a mold having a mold cavity whose profile corresponding to a desired profile of the contact lens. The contact lens of the invention may also be manufactured by injection molding, or alternatively by cutting in which a desirably shaped contact lens is cut out from a lens blank by utilizing techniques of turning. Further, a polishing process may be performed on the present contact lens as needed, like in the general process of manufacturing contact lenses.